Combustion gas generator of the free-floating piston type



Oct. 15, 1963v K. HELLWEG 3,106,913

coMBUsTloN @As GENERATOR oE THE FREE-nomma PIsToN TYPE Filed June 5, 1961 United States Patent O 3,106,913 COMBUSTION GAS GENERATR F THE FREE-FLATING PISTN TYPE Kurt Hellweg, La Fontaine, Antony, Seine, France, as-

signor to Socit Civile pour lEtude dlngins Pistons Libres EPL, Montreuil, Seine, France, a company of France Filed .lune 5, 1961, Ser. No. 114,329 Claims priority, application France `lune 8, 196i? 6 Claims. (Cl. 12.3-46) This invention relates to combustion gas generators of the 4type including a pair of tree-Heating motor pistons mounted for opposite reciprocation in a cylinder and having means `for injecting and igniting fuel in the cylinder space between the pistons, thereby propelling the pistons outwardly; during their outward stroke the pistons uncover an exhaust port through which the combustion gases, together with scavenging air delivered into said space by suitable means, is discharged under high pressure to receiver apparatus, such as a gas turbine. On the subsequent return stroke of the pistons, they act to compress a fresh char-ge of combustible gases and air.

'In generators of this type it is customary to associate with the motor pistons respective compressor pistons rigidly interconnected with the motor pistons and operating in respective compressor cylinders, so that the energy developed by the resulting piston units on their outbound stroke serves Ito compress a body of air, drawn into the compressor cylinders during the inward stroke of the piston units, which compressed air lis delivered into the motor cylinder between the motor pistons to full the combustion and scavenging Ifunctions.

In order to propel the piston units from their outer dead center positions on their inbound compression stroke, means are provided ior entrapping bodies of air which are .compressed on lthe outward stroke of the piston units and serve as resilient air cushions to return the units by their elasticity.

yIt is one object of this invention to provide |an improved arrangement for the said air cushioning means whereby the latter can be conveniently and etlioiently compressed by the outer end faces of the motor pistons themselves.

Gas generators of the type to which lthe invention relates must be capable of operating at widely varying pressures of scavenging lair and exhaust or output lgas pressures the variation in output pressure being 'fob-tained by correspondingly controlling the length of stroke of the motor pistons.

It is essential for a successful and eflicient operation of such generators throughout its operating range, that the requisite degree of compression 'be achieved by the motor pistons regardless of the exhaust pressure and length of stroke, and that said degree of compression shall not be less than a minimum value required for etcient combustion of the fuel but shall not exceed a safe maximum. Objects of this invention are to ensure that these results shall be positively obtained over la wide operating range.

Another object of the invention is lto provide that fthe degree of motor compression shall be low lfor low scavenging yair pressures tand 'correspondingly higher for high scavenging air pressures. The ladvantage of such operation is that the number of reciprocations of the free-floating pistons of the generator is proportional to the pres-sure differentials acting across the pistons, and that it is desirable to obtain a maximum number of reciprocations in the full load condition when the scavenging lair pressure is itself a maximum. The invention therefore accomplishes the further objects just specified.

Another object is to improve the operating stability in combustion lgas generators of the free loating type throughout a Iwide operating range.

3,l%,9l3 Patented Oct. 15, 1963 ICC The above and `further objects of the invention and the novel features thereof will appear yas the description proceeds. An exemplary embodiment of the invention will now be described with reference to the accompanying drawing, which is a simplified view mainly in axial cross section of an improved gas generator of the ree-lloatng piston type constructed .in accordance with the fea-tures of the invention.

The apparatus shown comprises 'a pair of similar, symrnetricallyv disposed reciprocatory units each comprising a motor piston 1 and 1', a piston rod 2 and 2', Iand a cornpressor piston 3 and 3 of larger diameter than the motor piston. The piston rod 2 or 2 is of substantially smaller diameter, preferably `less than half the diameter, of the motor piston 1 or 11. The two reciprocatory units are slidably mounted with the motor pistons 1 and 1 facing each other, in a casing assembly of complex shape which will be made clear as the description proceeds. The casing assembly includes la cylindrical portion 4 or common motor cylinder in which the motor pistons 1 and l1' are slidable, and formed with one or more scavenger ports 5, exhaust ports 6, land so called communication ponts includingffthe ports 7 on the same side as the scavenger ports and the ports 8 on the same side as the exhaust ports. The motor casing portion 4 includes end walls 9 and 9 'formed -with `central apertures including ring seals 10 and dit through which the respective piston rods sealingly slide. Defined between the outer side :11, 11 of each motor piston and the related end vvall 9, 9', is an fair cushion space or chamber l2, 12.

The casing structure further includes a pair of spaced compressor cylinder sections and 13 within which the compressor pistons y3 and 3 are respectively slidable. The outer end walls of the compressor cylinders are each provided with one or more inwardly opening air intake valves 14 and 14 provided with suitable spring `biassing means not shown. 'In the side walls `of each compressor cylinder 13 and 13 near the outer end thereof are outwardly opening lair discharge valves 15 and 1S' which may be similarly spring biassed. The air discharge Valves 15 and 15 open outwardly into annular channels 16 and 1-6' respectively which surround the outer ends of the compressor cylinders .13 and 13. The inner ends of the annular channels 16 and 16 communicate through longitudinal conduits 1S and 18 with a common centrally defined space 17 which may be ltermed the scavenging air reservoir. lt may already be indicated at this point of the description that 'on the inward stroke of both piston units, the compressor pistons 3 and 3 draw in 'air from the atmosphere through the air intake valve-s 14 and '14', and on the subsequent outward stroke the compressor pistons discharge this indrawn air through the discharge valves 15 and 15 and through conduits 18 and 18 respectively into the common scavenging air reservoir 17.

From each of the annular end channels 16 and 16' another longitudinal channel :or conduit 19 and 19' leads int-o a related one of two axially spaced annular casing sections 21 and 22 respectively surrounding the motor cylinder casing 4 in the areas thereof including the communioation ports 7 fand 8. Each of the two conduits 19 `and 19' is surrounded on part of its length by a heatexchanger 2li or Ztl respectively, provided with inlet and outlet means for a suitable cooling agent. The annular spaces 21 and 22 are separated, as shown, from the adjacent inner ends of the compressor cylinder spaces defined in the casing sections 13 and 13 by transverse .'walls 24 and Z4 respectively. The variable spaces or capacities 25, 25 defined between each of these walls 24, Z4 and the adjacent side suriace 23 or 23 of the compress-or pistons 3 and 3', are provided with outwardly opening springebiassed valves 26, 26' which discharge to atmosphere.

encanta Supported centrally of the casing structure is a radially disposed fuel injector 27 and associated fuel igniter means may be provided if required.

Description of an operating cycle of the apparatus is started with the instant when both the reciprocatory piston units are positioned at the inner dead centre position substantially as shown. Fuel is injected into the motor cylinder casing 4 between the motor pistons 1 and 1 by the fuel injection nozzle 27 and is ignited. The pressure of the expanding combustion gases acting on the inner end faces of pistons 1 and 1 propels both piston units outward. rl`he outer end faces 11 and 11' of the motor pistons almost immediately seal the communication ports 7 and 8 respectively, so that air is entrapped in the cushioning spaces v12 and l12 and is there compressed. At the same time, outward movement of the piston structures causes an increase in the volume of both capacities 25 and 25 thereby creating subatmospheric pressure in the capacities. Simultaneously the outer end faces of the compressor pistons 3 and 3 act as earlier described to discharge air previously drawn in from the atmosphere through air intake valves 14 and 14', outwardly through the discharge valves 1S and 15', into annular channels 16 and 16'. From the annular channels part of this air is delivered through conduits 18 and 18 into the scavenging air reservoir 17, while another portion of said air is passed through the conduits 19 and 19 past the coolers 20 and 20 into the spaces 21 and 22. As the motor pistons 1 and r1', proceeding on their outward or motor stroke, uncover the scavenging intake port and then the exhaust port 6 respectively, the air thus delivered to the scavenging air reservoir 1'7 is passed into the motor cylinder space between both motor pistons, scavenges or flushes out said space of the burned gases therein, and the mixture of gases and scavenging air is discharged through the exhaust port and conduit 6 to the utilization unit, such as a turbine, not shown.

In cases where the system is being operated in the upper region of its power range, and consequently the reciprocatory stroke of the piston units is of substantially maximum length, such that the outer dead centre positions of the motor piston are then as indicated for piston 1 in chain lines on the drawing, it will be noted that the inner end surfaces of the motor pistons `1 and l1' uncover the communication ports 7 and 8 respectively. This allows an additional amount of cool air to enter the motor cylinder space between pistons 1 and 1 from the annular spaces 21 and 22, cooling the hot inner ends of the motor pistons and contributing to increase the scavenging rate and reducing the temperature of the air and gases in the motor cylinder.

Further, as the motor pistons 1 and 1 approach the end of their outward stroke and after their outer end surfaces have sealed the communication ports 7 and 8 respectively said outer end surfaces act to compress the bodies of air entrapped beyond said ports in the spaces 12 and 12. These provide damping air cushions which store energy as pressure in the space 12 and 12 to cushion or dampen the rebound of the pistons from their outer dead center positions, and restore said energy to propel the pistons on their inward stroke, until the ports 7 and 8 have been uncovered by the outer end faces 11 and 11 of the pistons -1 and 1', whereupon said entrapped air cushions are again connected with the spaces 21 and 22 which are maintained at the scavenging air pressure as determined by the bias of valves and 15.

On the inward or return stroke of the pistons, both capacities 25 and 25 contract in volume, and the pressure therein rises till it again substantially attains atmospheric pressure. Any excess air that may have entered said capacities is discharged to atmosphere through the one-way valves 26 and 26'. When the pistons have reached their inner dead center position therefore the spaces 2S and 25 is always maintained at slightly superatmospheric pressure as determined by the bias of valves 26 and 26'.

It will be understood from the above that during the inward stroke the compressed air in the clearance space expands substantially to atmospheric pressure, and thereafter the compressor draws in a fresh amount of air by way of the intake valves 14 and 14'. During the inward stroke the inner end faces of motor pistons 1 and 1' first seal off the communication ports 7 and 8, then seal off the scavenging intake port 5, and finally seal off the exhaust port 6. At this point the compression stroke of the cycle sets in, and lasts until the inner dead center position has been reached when a fresh amount of fuel is injected and ignited to initiate a further outward motors stroke in the next cycle.

The combustion gas generator described has a number of important advantages. Owing to the provision of the so-calied communication ports 7 and the pressure in each of the air cushions in spaces 12 and 12 at the inner dead centre position of the cycle is always equal to the scavenging air pressure maintained in the related spaces 21 and 22 respectively by the valves 15 and 15', even though the compressor piston 3 and 3 at this time are only exposed to atmospheric pressure as they act to draw in scavenging air for the next cycle. It should be noted that the exhaust gas pressure supplied from the generator to the turbine or other receiver determines in turn the scavenging air pressure in the motor cylinder between motor pistons 1 and 1' and hence determines the pressure in scavenging reservoir 17 and also in the compressor cylinders 13 and 13', in conduits 19 and 19', capacities 22 and 22' and the air cushion spaces 12 and 12' when these spaces are maximum in volume. Owing to the resulting equality between the air cushion pressure and the scavenging air pressure, the result is obtained that the piston restoring force developed on expansion of the air cushions will be the stronger as the exhaust gas pressure is high. This is obviously desirable since when exhaust pressure is higher a stronger force must be exerted to ensure adequate compression of the air for the next combustion cycle. This feature of the invention greatly enhances the operating stability of the generator over its output range.

Another important feature of the invention lies in the provision of the communication ports 7 and 8 at such positions in the motor cylinder walls, and so predetermined with regard the axial length of the motor pistons, that the inner end faces of the motor pistons 1 and 1 will uncover said ports as they approach their outer dead center positions, in case of a long operating stroke, whereupon an additional amount of cool scavenging air is delivered to the cylinder. This cool air serves to lower the temperature of the hot inner ends of the motor pistons and protects the piston rings against overheating, while at the same time lowering the temperature of the remaining air present in the motor cylinder after the scavenging and exhaust ports have been sealed olf. The additional amount of scavenging air participates in the ensuing cornbustion, enhancing the thermal efficiency and increasing the available power output.

Another advantage of the communication port 8 positioned on the side of the motor cylinder adjacent, and beyond, the exhaust port 6, is that the combustion gases that tend to cling to the inner end face of the motor piston 1 are effectively swept away by the scavenging air supplied through said port S.

The provision of the exhaust valves 26 and 26' in the inner ends of compressor cylinders 13 and 13 serves to create a subatmospheric pressure in said ends of the compressor cylinders as the compressor pistons 3 and 3 are moving outwards, and this partial vacuum is then blocked within the cylinders by the closure of valves 26 and 26 on reversal of the piston movement so as to participate in exerting a propulsive force tending to return the piston units towards their inner dead centre positions.

As a result of the above features combustion gas generators constructed in accordance with the invention have been found to operate more eiciently and satisfactorily than comparable machines of the prior art. It should be understood that the embodiment of the invention shown and described is illustrative only and that various modiiications may be made therein within the scope of the ensuing claims.

What is claimed is:

1. In a combustion gas generator means defining cylinder structure; a pair of floating piston units oppositely reciprocable in the structure and each including interconnected motor and air compressor pistons; fuel means connected with the structure between the motor pistons for propelling said units outward; scavenger air intake chambers deined by said structure adjacent the compressor pistons and outwardly thereof including intake valve means for drawing air into said intake chambers during an inward stroke of the units; scavenger port means in the structure connected with the intake chambers and positioned to be uncovered by a motor piston during the outward stroke of the units; an exhaust port in the structure positionedto be uncovered by a motor piston during said outward stroke for discharging combustion gases and air to a point of use; damping air chambers defined in the structure adjacent the motor pistons and outwardly thereof; and further port means in said structure positioned to be uncovered by a motor piston in an inner dead center position of the units to connect the damping chambers with the scavenging air intake chambers for equalizing the pressure therebetween, said further port means being positioned to be uncovered by a motor piston in an outer dead center position of the units when said outward stroke of the units exceeds a predetermined minimum, to connect the intake chambers with the space between the motor pistons to provide additional air therein.

2. In the combination claimed in claim 1, rst passage means connecting said scavenger port means with said intake chambers, and separate second passage means connecting said further port means with said chambers.

3. In the combination claimed in claim 2, cooling means 6 associated with said second passage means for cooling the air-ow therethrough.

4. In the combination claimed in claim 2, one-way Valve kmeans controlling the flow from said intake chambers to said scavenger intake port and to said further port means, respectively.

5. In an internal combustion-free piston engine comprising an engine cylinder having scavenging ports and exhaust ports, a pair of free pistons in said cylinder, two compressor cylinders positioned one at each end of said engine cylinder, a compressor piston in each compressor cylinder and means interconnecting the engine and compressorpistons, two compensating air-cushion chambers formed by said engine cylinder, the air cushions in said chambers being compressed by said pistons during the outward stroke thereof, tirst additional ports in said engine cylinder between said scavenging ports and the cylinder end next the scavenging ports, second additional ports in said engine cylinder between said exhaust ports and the other cylinder end, and means for conducting compressed air from said compressor cylinders to said first and second additional ports, said lirst and second additional ports being positioned so as to communicate with the engine cylinder space between the free pistons only when the latter have been moved to substantially an extreme outer position thereof.

6. An internal combustion-free piston engine according to claim 5, in which said means for conducting compressed air to said first and second additional ports include a pipe section extending through cooling means adapted to cool the air flowing through said pipe section.

References Cited in the le of this patent UNITED STATES PATENTS Denmark Aug. 30, 1937 

1. IN A COMBUSTION GAS GENERATOR MEANS DEFINING CYLINDER STRUCTURE; A PAIR OF FLOATING PISTON UNITS OPPOSITELY RECIPROCABLE IN THE STRUCTURE AND EACH INCLUDING INTERCONNECTED MOTOR AND AIR COMPRESSOR PISTONS; FUEL MEANS CONNECTED WITH THE STRUCTURE BETWEEN THE MOTOR PISTONS FOR PROPELLING SAID UNITS OUTWARD; SCAVENGER AIR INTAKE CHAMBERS DEFINED BY SAID STRUCTURE ADJACENT THE COMPRESSOR PISTONS AND OUTWARDLY THEREOF INCLUDING INTAKE VALVE MEANS FOR DRAWING AIR INTO SAID INTAKE CHAMBER DURING AN INWARD STROKE OF THE UNITS; SCAVENGER PORT MEANS IN THE STRUCTURE CONNECTED WITH THE INTAKE CHAMBERS AND POSITIONED TO BE UNCOVERED BY A MOTOR PISTON DURING THE OUTWARD STROKE OF THE UNITS; AN EXHAUST PORT IN THE STRUCTURE POSITIONED TO BE UNCOVERED BY A MOTOR PISTON DURING SAID OUTWARD STROKE FOR DISCHARGING COMBUSTION GASES AND AIR TO A POINT OF USE; DAMPING AIR CHAMBERS DEFINED IN THE STRUCTURE ADJACENT THE MOTOR PISTONS AND OUTWARDLY THEREOF; AND FURTHER PORT MEANS IN SAID STRUCTURE POSITIONED TO BE UNCOVERED BY A MOTOR PISTON IN AN INNER DEAD CENTER POSITION OF THE UNITS TO CONNECT THE DAMPING CHAMBERS WITH THE SCAVENGING AIR INTAKE CHAMBERS FOR EQUALIING THE PRESSURE THEREBETWEEN, SAID FURTHER PORT MEANS BEING POSITIONED TO BE UNCOVERED BY A MOTOR PISTON IN AN OUTER DEAD CENTER POSITION OF THE UNITS WHEN SAID OUTWARD STROKE OF THE UNITS EXCEEDS A PREDETERMINED MINIMUM, TO CONNECT THE INTAKE CHAMBERS WITH THE SPACE BETWEEN THE MOTOR PISTONS TO PROVIDE ADDITIONAL AIR THEREIN. 